1. Field of the Invention
The present invention relates to a method for manufacturing a quartz glass ingot, especially for manufacturing a quartz glass slab ingot, and further relates to a method for manufacturing a round bar or a plate quartz glass ingot containing OH, which is useful as a material for semiconductor manufacturing equipment.
Further, the present invention relates to a quartz glass burner installed in a quartz glass manufacturing apparatus.
2. Prior Arts
There are many methods for manufacturing a quartz glass ingot by fusing silica powder, in which the heat is supplied by a flame of hydrogen-oxygen or a flame of propane-oxygen, an arc, or by electric heat. In general, as shown in Japanese patent Sho46-42111 (1971-42111,B2,JP), a quartz glass ingot is manufactured by fusing silica powder, depositing the fused silica on a rotating target, lowering the target gradually at a constant speed, and quenching the fused silica thereby forming a shell-like column ingot on the target. As disclosed in Kokai Hei 04-325425, (1992-325425,JP,A), silica powder is fused by a plasma arc and the fused silica is deposited on a rotating table, then a column quartz glass ingot is formed on the rotating table. Either of the finished quartz glass ingot has a form of a column.
In Kokai Sho 47-41640(1972-41640,A,JP), or in Kokai 52-145422(1977-145422,a,JP), there is disclosed a method of manufacturing a round bar quartz glass directly by fusing silica powder without a secondary heating process of a quartz glass ingot, in which silica powder is introduced into a furnace, fused therein and then fused silica is withdrawn from the bottom of the furnace continuously. The heat source of these methods is an electric heater disposed inside or outside the furnace.
A conventional method of manufacturing a round bar or a rectangular bar by using an oxygen-hydrogen flame as a heat source involves, first manufacturing a quartz glass ingot with an oxygen-hydrogen flame, then drilling a core glass mechanically from the ingot, or as disclosed in Kokai Sho 48-12319(1973-12319,A,JP), a previously formed quartz glass cylinder, which is placed in a case, is heated in an induction furnace or in a Tanman furnace at 2000 degrees centigrade, melted, and withdrawn from a nozzle to obtain a round bar or a rectangular bar. The conventional methods require a secondary process, therefore the process is called a two-step-manufacturing method.
In addition, in the methods of manufacturing a quartz glass by utilizing a flame as a heat source, it is not preferable to use a metal burner, because the metal burner releases a metal vapor or metal oxide which become impurities in the quartz glass.
A propane gas may be used for the flame fusing method of manufacturing quartz glass, but from a view point of the purity of the quartz glass, control of the atmosphere of the furnace or quality of the quartz glass, the oxygen-hydrogen flame manufacturing method is superior to the propane gas method.